Full-waveform inversion (FWI) is a tool for deriving velocity models in areas with complex geological conditions. FWI may be implemented in the time domain or in the frequency domain (FD FWI). Each realization has some advantages and disadvantages. For example, FD FWI can allow obtaining satisfactory results by hierarchical inversion of a small group of low frequencies. One difficulty of FD FWI is the lack of an efficient frequency domain solver. Ideally, the solver should be oriented for situations which may be described briefly as: 3D+elasticity+anisotropy+attenuation. Computing wave, even in isotropic cases, fields using a 3D frequency-domain solver in such a case can be complicated because huge linear systems must be solved. In such instances, iterative solvers can be more beneficial compared to direct solvers, for example, due to lesser memory requirements.